Process for improving the stability of cis-1 4-polyisoprene vulcanisates

ABSTRACT

PROCESS FOR IMPROVING THE STABILITY OF CIS-1,4-POLYISOPRENE VULCANISATES BY INACTIVATING A CATALYST CONTAINING SOLUTION OF POLYISOPRENE IN AN ORGANIC SOLVENT WITH A MIXTURE COMPRISING A LOWER ALIPHATIC ALCOHOL, A CONVENTIONAL ETABILISER AND A SMALL QUANTITY OF AN ALIPHATIC OR CYCLOALIPHATIC SECONDARY AMINE WHOSE ALKYL OR CYCLOALKYL RADICALS TOGETHER CONTAIN AT LEAST 10 CARBON ATOMS.

United States Patent US. Cl. 26094.7 N 3 Claims ABSTRACT OF THE DISCLOSURE Process for improving the stability of cis-1,4-polyisoprene vulcanisates by inactivating a catalyst containing solution of polyisoprene in an organic solvent with a mixture comprising a lower aliphatic alcohol, a conventional stabiliser and a small quantity of an aliphatic or cycloaliphatic secondary amine whose alkyl or cycloalkyl radicals together contain at least carbon atoms.

This application is a continuation of application Ser. No. 771,663 filed Oct. 29, 1968 and now abandoned.

It is known that isoprene can be polymerised with organo-metallic mixed catalyst of the Ziegler type, to give a product with a structure resembling that of natural rubber and having cis-1,4-linkages. vulcanisates of these polyisoprenes, however, differ from corresponding natural rubber vulcanisates so far as their properties in critical fields of application are concerned. Natural rubber is superior to commercial cis-1,4-polyisoprene in its cross-link yield and cross-link structure, as reflected in improved tensile strength and structural strength of the vulcanisates, in combination with higher strain values. This applies in particular to unfilled or weakly filled vulcanisates containing weak strengtheners, for example MT-carbon blacks, and is less pronounced but nevertheless still recognisable in HAF- and ISAF carbon black-mixtures of tread quality for vehicle tyres.

The polymerisation of isoprene with organometallic mixed catalysts, for example Al(i-C H /TiCl is known. The reaction is usually carried out in solution. For example, the following procedure may be adopted:

The catalyst is added to an 8 to 30% by weight solution of isoprene in an aliphatic or aromatic hydrocarbon in the absence of oxygen and moisture. Suitable solvents include, for example, pentane, hexane, cyclohexane, benzene and toluene. Mixtures of aluminium trialkyls, optionally in conjunction with their etherates and titanium tetrachloride may, for example, be used as the catalysts. Polymerisation may be carried out at temperatures from about to +80 C. After the required monomer conversion rate, for example 90% or more, has been attained, the catalyst can be inactivated by the addition of suitable substances, for example alcohols such as methanol or ethanol. Following the addition of suitable stabilisers, for example 2,6-di-tert.-butyl-4-methyl phenol; 2,2- dihydroxy 3,3 di tert.-butyl-5,5'-dimethyl diphenyl methane or phenyl-fl-naphthylamine, the polymer may be isolated from the solution by the addition of a precipitant, for example ethanol or acetone. On a commercial scale, the polyisoprene is usually recovered from the hydrocarbon solution by steam distillation (stripping). The rubber which is obtained in the form of crumbs is dried in a vacuum cabinet, either on a plate conveyor or by means of a screw.

It has now been found that cis-1,4-polyisoprene with improved properties can be obtained by inactivating a ice mbred-catalyst-containing solution of polyisoprene in an organic solvent, by means of a mixture of a lower aliphatic alcohol, a conventional stabiliser and a small quantity of an aliphatic or cycloaliphatic secondary amine, whose alkyl or cycloalkyl radicals together contain at least 10 carbon atoms.

Solutions of polyisoprene in organic solvents containing mixed catalysts include, in particular, the solutions referred to earlier on, of the kind that are directly formed during polymerisation. The inactivating agent according to the invention preferably comprises a lower aliphatic alcohol, for example methanol or ethanol, a conventioanl stabiliser and a small quantity of an aliphatic or cycloaliphatic amine which together are dissolved in an organic solvent, preferably the solvent of the polyisoprene solution. Suitable amines include in particular aliphatic or cycloaliphatic amines containing one fairly long chain and one shorter alkyl or cycloalkyl radical. Derivatives of methylamine in which one of the hydrogen atoms is replaced by a linear or branched alkyl radical with from 9 to 24 carbon atoms, are particularly suitable. Examples of suitable amines include di-Z-ethylhexylamine, dicyclohexylamine and N-stearyl methylamine. The amine is preferably used in a quantity of from 0.2 to 0.7% by weight, based on solid rubber.

The lower aliphatic alcohols employed, for example methanol or ethanol, are generally used in a quantity of from 0.2 to 5% by weight, based on rubber.

Examples of suitable stabilisers, which are generally used in a quantity of from 0.1 to 2% by weight, based on rubber, include 2,6-di-tert.-butyl-4-methylphenol; 2,2-dihydroxy-3,3-di-tert.-butyl-5,5'-dimethyl diphenyl methane and phenyl-B-naphthylamine.

The three compounds are usually added to the polyisoprene solution still contaim'ng an active catalyst in as concentrated as possible (for example, with a concentration of from 2 to 25% by weight) a solution in an inert solvent. The stabiliser may also be subsequently included in the mixture separately from the other compounds.

The resulting solution is Worked up in the usual way, for example by distillation with steam.

This method of inactivating the catalyst gives polyisoprene whose vulcanisates show distinctly improved properties and a reduced tendency towards reversion.

The improvement in the stability of the vulcanisate, i.e. the reduction of its tendency towards reversion, occurs above all in the critical, i.e. unfilled or inactively filled mixtures, and is also apparent, though not quite so noticeably, in vulcanisates containing ISAF- or HAF-carbon black. Further improvements are obtained in the scorch time and above all in the optimum values for tensile strength and structural strength, coupled with high strain values, and in the resistance to reversion in every vulcanisate ageing process, for example starting with the high temperature vulcanisation of highly dimensioned products and extending up to dynamic permanent stress, for example in tyres for heavy lorries.

The cis-l,4-polyisoprene rubbers obtained by the process according to the invention come more closely to the properties of good natural rubbers (RSS N.l) than commercial cis-l,4-polyisoprenes.

The polyisoprenes produced in accordance with the invention may be used for any purpose for Which high quality rubber is required, i.e. in particular for rubber products subject to high dynamic stressing, for example lorry tyres,

EXAMPLE 1 Polymerisation Isoprene was polymerised in 10% by weight solution in n-hexane in the presence of an organometallic mixed catalyst based on TiCl, and Al(C H 3 Working-up The polymerization mixture (conversion 93%=93% solids content) was divided. One part (Polymer A) was inactivated and stabilised with a mixture of 10% by weight of hexane, 2.5% by weight of ethanol and 1% by weight of 2,6-di-tert.-butyl-4-metl1ylphenol (based on polyisoprene). The second part of the mixture (Polymer B) was inactivated and stabilised with a mixture of 10% by weight of hexane, 2.5% by weight of ethanol, 0.5% by weight of N-methylstearylamine and 1% by weight of 2,6-di-tert.-butyl-4-methtylphenol (based on polyisoprene).

In order to test and assess the vulcanisation properties Mixture containing thermal carbon black MT This mixture, with its inactive carbon black filling (weakly acid), and weakly basic accelerator system, makes it relatively easy to differentiate between the eifects of the various inactivating and stabilising agents. The inactive filler does not disguise the differences in the properties, as is frequently the case, for example, with active fillers from the HAF or ISAF group. This test mixture responds particularly critically to changes in the quality of the polymers, owing to the well-balanced neutral adjustment of carbon black and accelerator. Both the level and reversion of the tensile strength and structural strength characterise the quality of the vulcanisate particularly clearly.

and the vulcanisates, the polyisoprene solutions. were 15 worked-up by steam distillation of the solvent after they Parts by had been inactivated and stabilised. The crumbs of rubber Formulation weight Processing o that were formed were dried in vacuo at 30 C. Rubber 10M Roller 400x200 mm" In the vulcanising tests, polymers A and B were comg1O 1 2.0 gems 40 earic aei .0 ric ion ParFd with a commiarclal product prepared Wlth the 20 Thermal carbon black T 30.0 r.p.m.24,mlxlng asslstance of a titanium catalyst (referred to as the 8 101110.. 2.5 time 22 min. commercial product) in a filler-free mixture (gum stock) 8:; and thermal carbon black MT-mixture and in the HAF carbon black mixture additionall with natural rubber. Tread ualit containin HAP carbon black 25 Detalls of the tests The property pattern of any general purpose rubber would not be complete without its test with active car- (1) Gum St0ck EXamination of the Vulcanisates of bon blacks in mlxtures substantlally of tread quality of the gum stock is critical. The vulcanisation behaviour a lorry tyre- TPCSB tests am mtended to Produce Peak of the pure polymers is assessed here unfalsified by fillers 30 Values tenslle Strength and Structural Strength: and other mixture components, because only those chemi- Companled by Stram and hardness valuescals that are absolutely necessary for crosslinking are Partsby present. The results of the test throw some light, for Formulation weight Processing example, upon the crosslink yield that can be obtained Rubbw 100.0 Temnwo C" and upon the uniformity of the cellular structure. 35 0. .0 rotat onal speed giggle argd b 40qr.p.m., lllllglng Car on 56 1181100 I'll OI Highly aromatic mineral 10. 0 0 mins., evcrthlng N-phcnyl-N'-isopropylpexcept sulphur and I Parts by phenylenc diamine 1. 0 accelerator l min., Formulation weight Processing Phcnyl-a-naphthylamine g cleart1shaft 3mlions Sulphur emp y 5 mins. enzo- Rubber 100.0 R0llcr400 200,tomp, 40 Bcnzothiazyl-cyclohexylthiazyl-cyclohcxyl Z110 2.5 40 C.,r0tatinna1 sulphcnamide 0.5 sulpllcnamide Stearic acid. 1. 0 speed 24 1.p.rn., and sulphur are Sulpl1ur 2.0 friction 111.2, mixin mixed in on the Dibenzotliiazy p 0.7 time 7min. Batchoil Roller. Diplienyl gunnidine 0.3

TEST FORMULA: THERMAL CARBON BLACK MT Mooney- Vulc. Modulus Hard- ML 4/l 00 Deio (80) scorch 3 atms., F, kp/ K1655, Elflsto Stu, Product rubber mixture rubber GME 120 mins. em. percent 300% 500% 23/75 23l75 kp/4 mm.

Commercial p1'oduct. s6 20 1,375/30 28 175 755 21 50 41/43 64 71 185 650 37 101 40/50 70/70 13 150 615 00 /50 70/78 11 45 163 535 35 03 48/40 68/16 10 50 155 040 32 47/48 67/74 7 PolymcrA 85 20 1,275/20 45' 10 780 12 37 32/30 60/00 6 20 180 000 30 00 47/48 71/71 10 i2 i3 23 a 8 10:; 3/3 1 60 145 655 23 78 45/45 68/70 4 PolymerB 82 10 1325/33 31' 1 205 750 27 7; 24/48 60 73 22 2 550 30 8 5 72 77 20 30 102 650 37 112 48/40 72 77 15 45 180 040 36 107 46/48 71/76 12 60 170 050 32 00 45/47 68/74 10 TEST FORMULA: GUM STOCK Mooney- Vulc. Modulus Hard- ML 4/ 100 Dcl'o (80) scorch 3 atms., F, kp/ 055, E1351? Str., Product rubber mixture rubber 5ME mins. cm. percent; 300% 500% 23/75 23l75 lip/4 H1111.

Conuuercial product. 80 30 1, 375/30 10 10 103 830 12 21 37/37 80/75 20 20 180 775 13 20 38/40 75 80 21 30 155 750 13 28 38/40 74/77 20 45 055 13 28 38/30 74/77 10 60 140 800 12 24 38/38 71/77 18 Pol mer-A 85 35 1,275,215 33' 10 110 855 10 16 32/34 70/77 18 20 170 775 12 27 37/30 75/ 0 21 i2 122 a 3 3 3/3 3/3 2 00 705 11 24 36/78 73/75 18 Polyinel'B 81 35 1,325/33 23 10 815 12 23 37/37 76/77 22 i3 123 358 i3 22 28528 $9733 3% 45 775 15 30 30/30 75/76 20 00 175 700 13 28 30/38 72/70 10 TEST FORMULA: HAF CARBON BLACK Mooney- ML 47100" scorch Vulc. Modulus rubber Defo (80) ME 3 atms., F, D, Hardness, Elast. Str., Product mixture rubber mixture 120 mins. kp/em. percent 300% 500% 23I75 23/75 kp/4 mm Natural rubber 89 54 300/41 825/11 37 100 485 45 101 46/38 39/38 12 192 535 83 174 54/52 42 9 36 197 525 89 182 56/54 42/49 38 187 520 88 184 56/53 41/49 34 60 179 515 78 172 /52 41/47 32 90 181 500 83 176 54/51 40/46 32 Commercial product-.. 86 57 1, 375/30 825/11 41 10 47 530 21 44 35/32 34/33 6 20 186 570 76 156 5 53 41/48 36 30 195 560 83 169 56/55 41/50 34 45 181 545 78 159 56/54 41/48 27 166 535 151 55/53 40/47 24 166 545 70 148 52/53 39/47 25 PolymerA 85 50 1,275/26 725/11 45 10 10 720 5 25 20 170 660 58 51/50 42/48 32 Polymer B 82 52 l, 325/33 750/12 36' 10 29 505 10 23 32/38 32/28 6 20 210 575 81 172 54/53 44/52 38 30 210 550 187 55/54 4 54 38 45 200 540 86 177 56/54 54/44 35 60 185 535 78 167 55/52 43 9 30 90 540 7 168 55/50 42/47 26 TESTING THE OPTIMAL HEATING STAGES [Comparison between NR, 2. commercial product, Polymer A and Polymer B] TEST FORMULATION: HAF-CARBON BLACK MIXTURE Commer- Natural cial Polymer Polymer Crude Mixture rubber product A B ML 4 (100 C.) Defo (80 C.) Mooney Scorch Relaxation (1%)- 38. 8 24. 0 24. 0 28. 0 Taekmeter (stickiness).. 846 912 600 880 Optimal heating: 3073.0 atms.:

DIN abrasion:

40 grade emery 176 162 172 167 60 grade emery 102 93 124 113 Skid-resistance: wet 53 52 52.3 52. 5 De Mattie (bends= 10 Grazing, 50% failure 95 45 70 83 Grazing, 100% failure 144 71 85 132 Crack growth:

24 m/m 61 37 40 44 118 68 67 84 12 m/m 161 88 85 107 Compression Set, Moth. B ASTM:

70h.RI 9.1 5.5 4.7 4.9 31. 3 25. 1 29. 4 23. 5 65. 5 62. 2 60.1 59. 4 Ball disintegration.

Useful life (revolution) 19. 370 14. 580 13.535 17. 480 Temperature C. with revolution)..." 178/7, 830 183/6, 680 185/6, 680 181/756 Goodrich Plexometer 0.0875 inch:

T above RT after:

10 in 27. 5 30. 0 29. 0 26. 0 33. 5 36. 0 34. 5 31. 0 ins 36. 0 38. 0 36. 0 32. 0 Flow at RT in percent after:

10 mins 2. 4 +1.0 +1. 2 +1. 4 -3. 5 +0. 5 +0. 2 +0. 6 5. 7 1. 2 1. 5 0. 8

EXAMPLES 2 TO 8 The effect of secondary amines used according to the invention is compared in the following Examples 2 to 8 with a series of primary and tertiary amines with reference to the example of N-methylstearylamine. The polyisoprene solutions were prepared as in Example 1 and were treated with the following amines in the manner set 75 out in Example 1 2 *All amines are used in equivalent quantities.

The polymers of Examples 2 to 8 were tested for serv- 0.2 to by weight of methanol or ethanol, (b) 0.1 to iceability in the Test Formula containing thermal carbon 2% by weight of a stabilizer and (c) 0.1 to 0.7% by black MT (Thermax MT), cf. following table: weight of N-methylstearylamine.

TEST FORMULA: THERMAL CARBON BLACK MT Vulc. Modulus 3atn1s., F, Hardness, Elast., Str., Example Number Amine mins. kp/cm. percent 300% 500% 23/75 23/75 kp/4 mm.

3 nGaH NH, 10 175 715 21 67 46/46 /71 16 20 154 525 30 88 48/49 73/71 11 30 157 645 27 83 47/47 72/71 8 60 155 650 25 79 47/47 68/69 5 158 665 21 69 44 45 68 69 5 4 C H NH 10 165 660 29 88 48/49 71/70 16 20 140 585 32 49/50 74/73 9 30 147 600 32 93 48/49 70/69 7 60 146 610 32 91 48/48 68/69 5 90 610 27 83 46/47 56/68 4 5 (C HQ NH 10 170 675 24 80 46/45 71/71 17 20 170 620 35 101 49/49 73/73 7 30 160 660 35 103 48/48 71/72 5 60 155 615 29 93 48/48 71/71 a 4 90 148 620 27 88 45/47 70/69 4 5 (CzH5)3N 10 160 43/40 66/67 15 2o 26 48/48 71/71 6 30 20 46/47 70/70 5 60 30 45/46 66/68 4 90 45 43/45 65/67 4 7 C12H25N(CH3)2 10 153 44/40 66/67 15 20 162 48/48 70/69 13 30 47/48 67/58 11 60 120 47/47 65/68 7 8 CmHmNHCH; 10 186 685 27 83 43/46 69 72 7 20 175 505 40 121 49/71 72/73 14 30 175 590 41 120 49/50 71/73 7 45 600 37 111 48/49 70/72 5 60 163 685 37 111 48/49 70/72 5 90 600 32 101 47/48 69/71 5 Comparison of the vulcanisate data of Examples 2 to 8 2. The process of claim 1 wherein said catalyst is tishows that N-methylstearylamine (Example 8) provides tanium tetrachloride and aluminum triethyl. the most favourable values in regard to the crosslink yield 3. The process of claim 1 wherein said stabilizer is and cellular structure, as reflected in the high level of 2,6-di-tert.-butyl-4-methylphenol, 2,2'-dihydroxy-3,3'-distrength, coupled with high modulus and hardness values. 45 tert.-butyl-5,5-dimethyl diphenyl methane or phenyl-fl- Ammonia (Example 2) and the tertiary amines (Examples naphthylamine.

6 and 7) do not provide satisfactory vulcanisates. The References Cit d crosslink yield is not sufficient either. The primary amines (Examples 3 and 4) and diethyl amine provide slightly UNITED STATES PATENTS better crosslink yields, although they are nowhere near as 50 3,135,716 6/1964 Urane'ck good as the level of Example 8. Above all, the tendency 3,177,165 4/1965 Morris et 1- towards reversion (reduction in strength, strain and hard- 3,269,997 8/1965 YP M L ness values) is too great. Reversion is considerably re- 3,008,944 11/1961 WIISOII- duced by N-methylstearylamine (Example 8). 3,094,514 6/1963 Tucker- W l i 55 3,424,736 1/ 1965 Nudenberg.

prqcess for.produci.ng cis'l4'polyisoprene by JOSEPH L. SCHOFER, Primary Examiner polymerizing isoprene in an al1phat1c or aromatrc hydrocarbon with a catalyst comprising titanium tetrachloride HAMROCK, Asslstant Examlnfil and aluminum trialkyl or an etherate thereof, the im- U 5 cl R provement comprising inactivating the catalyst contain- 60 ing solution of cis-1,4-polyisoprene with a mixture of (a) 260-96 R, 94.3, 45.9 

